Recent years have seen the advent of solar photovoltaic systems as a major source of power generation, particularly in the residential sector, and this growth is set to further accelerate as installed prices for solar photovoltaic systems continue to drop. The efficiency of solar photovoltaic systems has become a very important consideration as more and more systems have been installed, and cost competitiveness makes it necessary to get as much value out of installed systems as possible. For instance, if one were to look at the ideal (expected) photovoltaic system output versus the actual output for a typical day it would likely be seen that the efficiency of the system is not 100% throughout the operating period and that (particularly during peak power periods) the actual output of the system does not approach the expected output.
Temporary causes for performance deficits (such as soiling) can be taken care of by regular maintenance, but such maintenance schedules can be optimized if the timing and rate of these temporary causes is better understood. At the same time, permanent and unavoidable factors (such as component aging and degradation) have to be understood in more detail in order to predict and maximize the long-term overall performance and expected output of these systems. Accurate modeling of the system can help to understand the degradation, however uncertainties due to variable operating conditions will limit the capabilities even of relatively accurate models. Accelerated aging tests, although standardized for component manufacture, also do not account for the different impacts of variable operating conditions and environmental impacts.
It is therefore of great value to have a simple way of monitoring and evaluating the full delivery chain of photovoltaic generation—from the moment electricity is generated in a solar panel, to the moment it is supplied to the home or electricity grid.